Conventionally, resin films such as cellulose acylate films, polycarbonate films and polyolefin films have been used as optical compensation films for liquid crystal displays. Thereamong, cellulose acylate films have been widely used since they have excellent compatibility with polyvinyl alcohol used as a polarizer.
However, cellulose ester films themselves do not have sufficient retardation (birefringence) required for an optical compensation film; therefore, a variety of methods have been examined for imparting a cellulose ester film with retardation. In addition, in recent years, increasingly large retardation has been demanded due to further expansion of viewing angle and reduction in thickness of liquid crystal televisions.
For improvement of the retardation of a resin film, a method of adding a retardation-increasing agent is known; however, it has been difficult to apply such a method into practice since conventional retardation-increasing agents are required to be added in a large amount and cause problems of bleed-out and the like. In addition, for example, a method of reducing the total acyl group-substitution degree of cellulose has also been proposed; however, practical application of this method is also difficult since there are problems of an increase in the moisture absorption and the like.
Under such circumstances, as a step toward practical application, methods of adding a specific retardation-increasing agent have been recently proposed. For example, in Patent Document 1, a phase difference plate which comprises a cellulose ester film containing a specific aromatic compound as a retardation-increasing agent is proposed. Furthermore, in Patent Document 2, a cellulose ester film in which a polycyclic aromatic compound having a phenolic hydroxyl group is used as a retardation-increasing agent is proposed. Meanwhile, in Patent Document 3, an UV filter element in which dibenzoylmethane is used as an ultraviolet absorber, not as a retardation-increasing agent, is proposed.